Mooren's ulcer is a painful peripheral corneal ulceration that can progress relentlessly to blindness. The pathogenesis of this disease remains unknown and the diagnosis is one of exclusion. An autoimmune etiology has been suggested involving a cornea-specific antigen (CO-Ag) that incites both a humoral and cell-mediated immune response. Understanding the auto immune etiology of the disease could result in earlier recognition of the disease and be of immense value in the development of specific treatment regimens. Aim 1: To map pathogenic epitopes within the CO-Ag protein. The amino acid sequence of CO-Ag has been determined. Overlapping peptides corresponding to the entire CO-Ag protein will be synthesized. Each peptide fragment will be tested for reactivity against serum antibody from Mooren's ulcer patients and patients with other corneal peripheral ulcerative diseases. Identification of a disease-specific epitope will lead to the development of a diagnostic test to differentiate Mooren's ulcer from other peripheral corneal diseases. Aim 2: To test the hypothesis that an immune response mounted by Mooren's ulcer patient against a particular determinant of an infectious agent may cross-react with a sequence of a disease-specific epitope of CO- Ag leading to corneal tissue injury and melting disease by the mechanism of molecular mimicry. Aim 3: To isolate and characterize a human cDNA clone with coding sequences for CO-Ag autoantigen. Synthetic oligonucleotide probes will be created on the basis of the known amino acid sequence of CO-Ag. These probes will be used to screen a human corneal fibroblasts cDNA library constructed in the expression vector UniZapXR. The CO-Ag cDNA clone will be used a hybridization probe to determine the level of COAg mRNA expression in different tissues on Northern blot analysis. Aim 4: To analyze the phenotype of the infiltrating cells, and to-use anti-granzyme antibody for detection of activated cytotoxic T-cells in patient's corneal tissues by immunocytochemical staining in attempt to understand the role of cytotoxic T-cells in the pathogenesis of Mooren's ulcer.